Help please pressure drop

[les luchini]

Evening all,
I have a Potterton Performa 28, 95% plumbed with JG Speedfit the system is 8 years old. Over the past few weeks the system has been losing pressure, done the usual of checking the rads for corrosion, rad valves all ok, lifted the inspection hatches and checked the manifolds all ok. no visible water marks on ceilings however their was black water mark stains in the downstaires hallway leading to a shower room. the flooring is weyroc throughout the house. I remember Teeing off the hall rad to feed the shower room other than these two Tee offs there are no more joins between the manifolds and the rads. So cut a channel in the weyroc
1ft x 8ft found nothing polystirene and plastic underneath also dry.
Boiler loosing between .5 and .75 of pressure overnight. filled the system again this morning 1.5 bar by mid afternoon had dropped to 1.2 bar the heating was not on. Help!!!!!!!!!!!!! new carpets coming on wednesday.

[WHPES]

Have you checked the expansion vessel and pressure relief valve? If the air has leaked out of the expansion bladder, water may be being lost as it expands.

[les luchini]

Thanks WHPES,
This was checked on Tuesday and set at 1.5 bar, have not checked it since.

[WHPES]

Put something under the oultet which will catch anything dripping and let you know.

[les luchini]

Sorry WHPES,
Forgot to say I uncoupled the pressure relif pipe put newspaper under the boiler no leaks news paper dry.

[gas man]

also the o rings on the heat exchanger of the performa go bang around this age but its probably the expansion vessel if its the o rings they cost £2 each and are a doddle if you know how to do them on the performa remove the top plate behind the boiler[4 screws] looking at the red disc[the expansion vessel]remove the dust cap and blip the shrader valve if no air in there re-presureise to 1 bar with a bike pump but you must drain the boiler to do this,as you will get a false reading if when you blip the shrader valve you find water the expansion vessel is toast and you need a new one of course this may also be the case if the membrane loses pressure again after you check it

[les luchini]

Thanks gas man,
not thought about that will give it a go on monday.